The equation of any plane passing through (1, 2, 3) is
a(x – 1) + b(y – 2) + c(z – 3) = 0
which is perpendicular to x = 0 and y = 0
So, a = 0, b = 0.
Thus, the equation of the plane is
c(z – 3) = 0
(z – 3) = 0
Thus, the required distance from (0, –1, 0) to the plane (z – 3) = 0 is